We propose to immunodetect, biochemically characterize and investigate the function of cell surface molecules which may be of importance in the interaction of cells with their environment. We will continue investigation of two molecules, a stage specific embryonic antigen (SSEA-1) and the human receptor for epidermal growth factor (rEGF) to which we have previously made antibody probes. We will test the hypothesis that a specific carbohydrate recognition molecule for SSEA-1 exists and that interaction between this receptor and SSEA-1 is a means of intercellular communication. We will also continue to investigate the rEGF, using our antibody probe to determine how EGF-rEGF interaction transmits the signal for cell proliferation. Using phosphotyrosine as a clue to detect molecules potentially involved in cellular proliferation, we will attempt to define changes in such molecules during differentiation of both human and murine teratocarcinoma-derived cells and to classify differences in such molecules on human hepatoma cell lines. Many of the cell lines necessary to do this work were derived by us and represent cells at unique stages of differentiation and function. Having categorized differences in the molecules containing phosphotyrosine residues we will attempt to isolate them and prepare antibody probes to determine their functional properties. Finally, we propose to biochemically characterize, genetically map and determine the function of a series of molecules for which we have antibody probes and to investigate the use of these monoclonal antibody probes in tumor diagnosis.